CN113328045A

CN113328045A - Light emitting device and light emitting apparatus

Info

Publication number: CN113328045A
Application number: CN202110590509.6A
Authority: CN
Inventors: 王斯琦; 孙海雁; 张晓晋
Original assignee: BOE Technology Group Co Ltd
Current assignee: BOE Technology Group Co Ltd
Priority date: 2021-05-28
Filing date: 2021-05-28
Publication date: 2021-08-31
Anticipated expiration: 2041-05-28
Also published as: CN113328045B

Abstract

The present disclosure provides a light emitting device and a light emitting apparatus, including: a light emitting layer and an electron blocking layer, the light emitting layer including a thermally activated delayed fluorescence material; the electron blocking layer comprises a material of structural formula (1):

x is N; y is O, S, Se; l is selected from arylene with 6-20 carbon atoms, and n is more than or equal to 1; the substituents R1-R8 are selected from H, C1-C12 alkyl, C6-C30 arylene or C3-C30 heteroarylene; r9, R10 are selected from structures of structural formula (2):

z is selected from N, O, S, Se; the substituents R11-R14 are selected from the group of H, C1-C12 alkyl, C6-C30 arylene or C3-C30 heteroarylene; ar is selected from arylene with 6-20 carbon atoms, biphenyl and naphthalene. The light emitting device and the light emitting device can improve OLEDExternal quantum efficiency and operating life.

Description

Light emitting device and light emitting apparatus

Technical Field

The present disclosure relates to the field of display technologies, and in particular, to a light emitting device and a light emitting apparatus.

Background

Full-color Organic Light Emitting Diodes (OLEDs) have a wide range of applications in full-color, flexible displays and space lighting. Of the three typical display colors, the red and green emitters have high External Quantum Efficiency (EQE) and long lifetimes, but the blue emitter performs relatively poorly. Therefore, Thermally Activated Delayed Fluorescence (TADF) OLEDs have been investigated in place of conventional blue fluorescent OLEDs. However, the short service life of the TADF-OLED limits its application.

Disclosure of Invention

The embodiment of the disclosure provides a light emitting device and a light emitting apparatus, which can increase the external quantum efficiency and the working life of a TADF OLED.

The technical scheme provided by the embodiment of the disclosure is as follows:

the disclosed embodiment provides a light emitting device, including:

an anode and a cathode disposed opposite to each other;

a light emitting layer disposed between the anode and the cathode, wherein a light emitting material of the light emitting layer includes a host material and a guest material, and the guest material includes a thermally activated delayed fluorescence material;

and an electron blocking layer disposed between the light emitting layer and the anode;

the electron blocking layer comprises a material of structural formula (1), wherein the structural formula (1) is as follows:

wherein,

x is N;

y is selected from O, S, Se;

l is selected from substituted or unsubstituted arylene with 6-20 carbon atoms, wherein n is more than or equal to 1;

the R1-R8 substituents are independently selected from H, C1-C12 alkyl, substituted or unsubstituted C6-C30 arylene, or substituted or unsubstituted C3-C30 heteroarylene;

r9, R10 are independently selected from the structures of structural formula (2), structural formula (2) is as follows:

wherein,

z is selected from N, O, S, Se;

the R11-R14 substituents are independently selected from the group consisting of H, C1-C12 alkyl, substituted or unsubstituted C6-C30 arylene, or substituted or unsubstituted C3-C30 heteroarylene;

ar is at least one selected from substituted or unsubstituted arylene with 6-20 carbon atoms, biphenyl and naphthalene.

Illustratively, in the structural formula (1), Y is O.

Illustratively, the material of the electron blocking layer is specifically selected from the following compounds:

illustratively, the light emitting device further comprises a hole transport layer disposed between the electron blocking layer and the anode;

the electron blocking layer, the light emitting layer and the hole transport layer satisfy the following conditions:

0.1eV＜∣HOMO_HTL-HOMO_EBL∣≤0.3eV；

0.1eV＜∣HOMO_EBL-HOMO_host∣≤0.3eV；

wherein,

HOMO_HTLis the highest occupied molecular orbital of the hole transport layer;

HOMO_hostis the highest occupied molecular orbital of the host material;

HOMO_EBLis the highest occupied molecular orbital of the host material.

Illustratively, the electron blocking layer has a T1 energy level at least 0.1eV higher than the T1 energy level of the guest material.

Illustratively, the | -HOMO of the electron blocking layer_EBL∣≥5.6eV。

Illustratively, the electron blocking layer has an S1 energy level greater than or equal to 3 eV.

Illustratively, the redox peak difference remains within a predetermined threshold value when the electron blocking layer is subjected to N electrochemical cyclic voltammetry treatments, N being an integer greater than or equal to 30.

Illustratively, the electron blocking layer has a hole mobility greater than 10^-3cm²V^-1s^-1。

Illustratively, the light emitting layer is a blue light emitting layer.

Illustratively, the doping ratio of the host material to the guest material is as follows:

the concentration of the main body material is 80-99.9%;

the concentration of the guest material is 0.1-20%.

The embodiment of the disclosure also provides a light-emitting device which comprises the light-emitting device provided by the embodiment of the disclosure.

The beneficial effects brought by the embodiment of the disclosure are as follows:

the light-emitting device and the light-emitting device provided by the embodiment of the disclosure construct a proper electron blocking layer material, the electron blocking layer material can be used in cooperation with a light-emitting layer of a TADF-OLED system, the molecular structure of the electron blocking layer material has good electrochemical stability, and the electron blocking layer material has a high T1 energy level, which is beneficial to preventing electron leakage and preventing exciton leakage in TADF; the electron barrier material also has a high S1 energy level, which is beneficial to preventing energy from flowing back; and a proper HOMO energy level can effectively perform energy level matching, and is beneficial to the improvement of External Quantum Efficiency (EQE) and the service life.

Drawings

FIG. 1 shows a schematic structural view of a light emitting device in some embodiments of the present disclosure;

fig. 2 shows cyclic voltammograms of an electron blocking layer material in a light-emitting device according to example 1 of the present disclosure;

fig. 3 shows cyclic voltammograms of an electron blocking layer material in a light-emitting device according to example 2 of the present disclosure;

fig. 4 shows cyclic voltammograms of the electron blocking layer material in the light-emitting device of comparative example 1;

fig. 5 shows emission spectra of the light emitting layers in the light emitting devices of the above-described example 1, example 2, and comparative example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure more apparent, the technical solutions of the embodiments of the present disclosure will be described clearly and completely with reference to the drawings of the embodiments of the present disclosure. It is to be understood that the described embodiments are only a few embodiments of the present disclosure, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the disclosure without any inventive step, are within the scope of protection of the disclosure.

Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. The use of "first," "second," and similar terms in this disclosure is not intended to indicate any order, quantity, or importance, but rather is used to distinguish one element from another. Also, the use of the terms "a," "an," or "the" and similar referents do not denote a limitation of quantity, but rather denote the presence of at least one. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.

Before the detailed description of the light emitting device and the light emitting apparatus provided in the embodiments of the present disclosure, it is necessary to describe the following related art:

in the related art, for full-color Organic Light Emitting Diodes (OLEDs), of the three typical display colors, red and green emitters have high External Quantum Efficiency (EQE) and long lifetimes, but blue emitters have relatively poor performance, and Thermally Activated Delayed Fluorescence (TADF) OLEDs can be used instead of conventional blue fluorescent OLEDs. However, the short service life of the TADF-OLED limits its application.

A major factor affecting the EQE and lifetime of an OLED is hole and electron leakage into the emissive layer, thereby confining carriers within the emissive layer. Two functions of the Hole Transport Layer (HTL) are to transport holes and to block electrons. Most HTL materials can only serve to transport holes without blocking electrons, and thus an additional Electron Blocking Layer (EBL) is added in designing a light emitting device to facilitate hole injection and limit electron leakage to improve efficiency and brightness of the OLED device. However, the EBL currently used for blue OLEDs does not solve the problem of short lifetime of TADF-OLEDs. Therefore, it is necessary to develop EBL to increase the EQE and operational lifetime of the blue TADF-OLED.

The embodiment of the disclosure provides a light-emitting device and a light-emitting device, which can be applied to a TADF OLED system, and can improve the external quantum efficiency and the service life of the TADF OLED.

As shown in the drawings, a light emitting device of an embodiment of the present disclosure includes:

an anode 100 and a cathode 200 disposed opposite to each other;

a light emitting layer 300 disposed between the anode 100 and the cathode 200, wherein light emitting materials of the light emitting layer 300 include a host material and a guest material, and the guest material includes a thermally activated delayed fluorescence material;

and an Electron Blocking Layer (EBL)400 disposed between the light emitting layer 300 and the anode 100;

the electron blocking layer 400 includes a material of structural formula (1), the structural formula (1) is as follows:

wherein,

x is N;

y is selected from O, S, Se;

wherein,

z is selected from N, O, S, Se;

In the light emitting device provided by the embodiment of the present disclosure, a suitable electron blocking layer 400 material is configured, the electron blocking layer 400 material can be used with the light emitting layer 300 of the TADF-OLED system, the electron blocking layer 400 material is selected from the materials of the structural formula (1), the molecular structure has good electrochemical stability, and the material has a high S1 energy level and a high T1 energy level, wherein, since the power blocking layer material has a high T1 energy level, it is beneficial to prevent electron leakage and prevent exciton leakage in TADF; the electron barrier layer 400 material also has a high S1 energy level, which is beneficial to preventing energy from flowing back; and a proper HOMO energy level can effectively perform energy level matching, and is beneficial to the improvement of External Quantum Efficiency (EQE) and the service life.

It should be noted that S represents a Singlet state of an electronic track (Singlet, i.e., two electronic matching directions of a key are opposite), and S1 represents a first Singlet state; t indicates that the electron orbital is Triplet (Triplet, i.e., the direction of the two electron matches for bonding is the same), and T1 indicates the first Triplet.

In some exemplary embodiments, in the structural formula (1), Y is O, which provides the EBL material with good electrochemical stability.

For example, the material of the electron blocking layer 400 is specifically selected from, but not limited to, the following compounds:

abbreviated a 1;

abbreviated a 2;

abbreviated a 3;

abbreviated a 4;

abbreviated a 5;

abbreviated a 6;

abbreviated a 7;

abbreviated A8;

abbreviated a 9;

abbreviated a 10;

abbreviated a 11;

abbreviated a 12;

abbreviated a 13;

abbreviated a 14;

abbreviated as a 15.

In addition, in some embodiments, the light emitting device further includes a hole transport layer 500 disposed between the electron blocking layer 400 and the anode 100; the material of the electron blocking layer 400 and the light emitting layer 300 and the hole transport layer 500 adjacent thereto also satisfy the following relationship:

0.1eV＜∣HOMO_HTL-HOMO_EBL∣≤0.3eV；

0.1eV＜∣HOMO_EBL-HOMO_host∣≤0.3eV；

wherein,

HOMO_HTLis the highest occupied molecular orbital of the hole transport layer 500;

HOMO_hostis the highest occupied molecular orbital of the host material;

HOMO_EBLis the highest occupied molecular orbital of the host material.

In the above scheme, the energy level relationship between the material of the electron blocking layer 400 and the adjacent light emitting layer 300 and hole transport layer 500 is effective energy level matching, which is beneficial to hole transport.

In addition, the T1 energy level of the electron blocking layer 400 is at least 0.1eV higher than the T1 energy level of the guest material, which is advantageous for preventing electron leakage and exciton leakage of TADF material in the guest material.

Furthermore, the | -HOMO of the electron blocking layer 400_EBL| > 5.6 eV. In this way, an efficient energy level matching is provided.

Illustratively, the electron blocking layer 400 has an S1 energy level greater than or equal to 3eV, which may be more advantageous in preventing energy from flowing back. This is because excitons formed on the host material in the light emitting device are transferred from S1 of the host material to S1 of the emitter by Forster energy transfer, and thus the energy level of S1 of the host material is higher than the energy level of S1 of the emitter to achieve energy transfer, and similarly, if the energy level of S1 of the electron blocking layer is lower than the energy level of S1 of the host material, energy transfer to the material of the electron blocking layer occurs, and thus, in the above scheme, the electron blocking layer is set to have a relatively high S1 energy level value, and meanwhile, the material satisfying the molecular formula also has an advantage of a high S1 energy level.

In addition, the redox peak difference value of the electron blocking layer 400 is maintained within a predetermined threshold value when the electron blocking layer is subjected to N electrochemical cyclic voltammetry processes, where N is an integer greater than or equal to 30.

A specific value of the predetermined threshold may be, for example, 0.15V, that is, a difference between redox peaks of the electron blocking layer 400 after N electrochemical cyclic voltammetry processes is within 0.15.

Further, the predetermined threshold may be 0.1V.

In addition, the electron blocking layer 400 has a hole mobility of more than 10^-3cm²V^-1s^-1。

In addition, of the three typical display colors, the red and green emitters have high External Quantum Efficiency (EQE) and long lifetimes, but the blue emitter performs relatively poorly. Therefore, Thermally Activated Delayed Fluorescence (TADF) OLEDs may be used instead of conventional blue fluorescent OLEDs.

In the light emitting device in some embodiments of the present disclosure, the light emitting layer is a blue light emitting layer. That is, the light emitting device of the embodiment of the present disclosure may be applied to a blue TADF OLED light emitting device.

However, the light emitting layer of the light emitter provided by the present disclosure may also be another color light emitting layer such as a red light emitting layer, a green light emitting layer, and the like.

In addition, in some embodiments, the doping ratio of the host material to the guest material in the light emitting layer 300 is as follows: the concentration of the main body material is 80-99.9%; the concentration of the guest material is 0.1-20%.

It is of course understood that, in practical applications, the guest doping ratio of the light emitting layer 300 is not limited.

As an exemplary embodiment, a stacked structure of a light emitting device provided by the embodiments of the present disclosure may include, as shown in fig. 1, sequentially disposed: an Anode 100(Anode), a Hole Injection Layer (HIL)600, a hole transport layer 500(HTL), an electron blocking layer 400(EBL), an emission layer 300(EML), a Hole Blocking Layer (HBL)700, an Electron Transport Layer (ETL)800, an Electron Injection Layer (EIL)900, and a Cathode 200 (Cathode).

It should be noted that, according to actual needs, other functional layers may be added to the structure of the light emitting device for modification, or some functional film layers may not be provided according to actual needs, for example, a hole blocking layer, a hole injection layer, and the like may not be provided.

In addition, it should be noted that the light emitting device may be a positive light emitting device, i.e., the bottom electrode is the anode 100 and the top electrode is the cathode 200; it may also be an inverted light emitting device, i.e. the bottom electrode is the cathode 200 and the top electrode is the anode 100. Accordingly, the light emitting device may be a top light emitting device or a bottom light emitting device.

In addition, the External Quantum Efficiency (EQE) and the lifetime of the light emitting device of the present disclosure will be described below by taking the fabrication of the light emitting device in the embodiment shown in fig. 1 as an example. Specifically, a comparative example and two examples were made in the present disclosure, wherein the comparative example is the same as the materials of the hole injection layer, the hole transport layer 500, the light emitting layer 300, the hole blocking layer, the electron transport layer, and the cathode 200 in each example, except that the material selected for the electron transport layer is different.

The following method may be specifically adopted to fabricate the light emitting device in the embodiment shown in fig. 1:

example 1:

in the first step, the vacuum degree is 1X 10^-5Depositing a film on a glass substrate containing an anode 100 of Indium Tin Oxide (ITO) and having the thickness of the ITO film of 100nm by a vacuum evaporation method under the regulation of Pa;

a second step of forming a Hole Injection Layer (HIL)600 on the substrate by vapor deposition, the hole injection layer having a thickness of 10 nm;

a third step of forming a hole transport layer 500(HTL) on the hole injection layer by vapor deposition, the hole transport layer 500 having a film thickness of 60 nm;

fourthly, evaporating a compound A1 on the hole transport layer 500 film layer to form an electron blocking layer 400(EBL) with the thickness of 10nm, wherein the compound A1 has the following structural formula:

fifthly, co-evaporating a host material (TM) and a guest material (dopant) on the electron blocking layer 400, and forming a luminescent layer 300(EML) with a thickness of 25nm, wherein the guest material comprises a thermally activated delayed fluorescence material (TADF), and the concentration of the host material in the luminescent layer 300 is 90% and the concentration of the doped guest material is 10%;

a sixth step of vapor-depositing an Electron Transport Layer (ETL)800 on the light-emitting layer 300 to a film thickness of 35 nm;

seventhly, evaporating LiF (lithium fluoride) on the electron transport layer to form an Electron Injection Layer (EIL)900, wherein the thickness of the film is 1 nm;

and an eighth step of depositing metal Al on the LiF film to form a metal cathode 200 having a film thickness of 80 nm.

Briefly describing the element structure of the light-emitting device of example 1, the stacked structure of the light-emitting device is as follows: ITO/HIL/HTL/A1/TM: dock/ETL/LiF/Al.

Example 2:

fourthly, evaporating a compound A7 on the hole transport layer 500 film layer to form an electron blocking layer 400(EBL) with the thickness of 10nm, wherein the compound A7 has the following structural formula:

Briefly describing the element structure of the light-emitting device of example 2, the stacked structure of the light-emitting device is as follows: ITO/HIL/HTL/A7/TM: dock/ETL/LiF/Al.

Comparative example 1:

in the first step, the vacuum degree is 1X 10^-5Under Pa regulation, the anode 100 is Indium Tin Oxide (ITO) with a thickness of 10ADepositing a film on a 0nm glass substrate by a vacuum evaporation method;

fourthly, a compound TCTA (tris (4-carbazolyl-9-ylphenyl) amine) is vapor-deposited on the hole transport layer 500 to form an electron blocking layer 400(EBL) with a thickness of 10nm, and the compound TCTA has the following structural formula:

Briefly showing the element configuration of the light-emitting device of comparative example 1, the stacked structure of the light-emitting device is as follows: ITO/HIL/HTL/TCTA/TM: company/ETL/LiF/Al.

Fig. 2 shows cyclic voltammograms of the material of the electron blocking layer 400 in the light-emitting device of example 1 described above;

fig. 3 shows cyclic voltammograms of the material of the electron blocking layer 400 in the light-emitting device of example 2 described above;

fig. 4 shows cyclic voltammograms of the material of the electron blocking layer 400 in the light-emitting device of comparative example 1 described above.

As can be seen from fig. 2 to 4, the light emitting devices of example 1 and example 2 of the present disclosure have improved electrochemical stability compared to the light emitting device of comparative example 1.

Fig. 5 shows emission spectra of the light emitting layer 300 in the light emitting devices of the above-described example 1, example 2, and comparative example 1.

As shown in fig. 5, in comparison with the light-emitting device in comparative example 1, the light-emitting devices in examples 1 and 2 of the present disclosure adopt a trap mechanism in the light-emitting layer, and the HOMO definition of the electron blocking layer, the S1 level and the T1 level allow energy to be efficiently trapped by the emitter in the TADF light-emitting layer, which efficiently emits light by its own ISC (inter system Crossing) and RISC (reverse inter system Crossing).

The material parameter characterization of the electron blocking layer 400 in the light emitting devices of the above-described example 1, example 2 and comparative example 1 is shown in table 1 below.

Device performance characteristics of the light emitting devices of the above example 1, example 2 and comparative example 1 are shown in table 2 below.

TABLE 1 Material parameters

TABLE 2 device Performance

	EBL material	EQE(％)	LT90(h)
				Example 1	A1	7.15	277
Example 2	A7	6.85	75
				Comparative example 1	TCTA	6.11	34

As can be seen from table 2, the light emitting devices provided in examples 1 and 2 of the present disclosure have improved EQE efficiency and lifetime compared to the light emitting device in comparative example 1.

It should be noted that the foregoing examples 1 and 2 are only for comparison with the comparative example 1, so as to illustrate that the light emitting device provided by the embodiment of the present disclosure can achieve the enhancement of EQE efficiency and lifetime of the TADF-OLED device. It should be understood that there is no list of materials that can be selected for the electron blocking layer 400 in the light emitting device, but this does not indicate that only the light emitting devices provided in embodiments 1 and 2 can bring the beneficial effects of the light emitting device of the present disclosure.

In addition, the embodiment of the disclosure also provides a light-emitting device which comprises the light-emitting device provided by the embodiment of the disclosure. Obviously, the display device provided by the embodiment of the present disclosure also has the beneficial effects brought by the light emitting device provided by the embodiment of the present disclosure, and details are not repeated herein.

The following points need to be explained:

(1) the drawings of the embodiments of the disclosure only relate to the structures related to the embodiments of the disclosure, and other structures can refer to the common design.

(2) For purposes of clarity, the thickness of layers or regions in the figures used to describe embodiments of the present disclosure are exaggerated or reduced, i.e., the figures are not drawn on a true scale. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "under" another element, it can be "directly on" or "under" the other element or intervening elements may be present.

(3) Without conflict, embodiments of the present disclosure and features of the embodiments may be combined with each other to arrive at new embodiments.

The above is only a specific embodiment of the present disclosure, but the scope of the present disclosure is not limited thereto, and the scope of the present disclosure should be determined by the scope of the claims.

Claims

1. A light emitting device, comprising:

an anode and a cathode disposed opposite to each other;

wherein,

x is N;

y is selected from O, S, Se;

wherein,

z is selected from N, O, S, Se;

2. The light-emitting device according to claim 1,

in the structural formula (1), Y is O.

3. The light-emitting device according to claim 2,

the material of the electron blocking layer is specifically selected from the following compounds:

4. the light-emitting device according to claim 1,

the light emitting device further includes a hole transport layer disposed between the electron blocking layer and the anode;

0.1eV＜∣HOMO_HTL-HOMO_EBL∣≤0.3eV；

0.1eV＜∣HOMO_EBL-HOMO_host∣≤0.3eV；

wherein,

HOMO_HTLis the highest occupied molecular orbital of the hole transport layer;

HOMO_hostis the highest occupied molecular orbital of the host material;

HOMO_EBLis the highest occupied molecular orbital of the host material.

5. The light-emitting device according to claim 1,

the electron blocking layer has a T1 energy level at least 0.1eV higher than the T1 energy level of the guest material.

6. The light-emitting device according to claim 1,

-HOMO of said electron blocking layer_EBL∣≥5.6eV。

7. The light-emitting device according to claim 1,

the electron blocking layer has an S1 energy level greater than or equal to 3 eV.

8. The light-emitting device according to claim 1,

the redox peak difference value of the electron blocking layer is kept within a predetermined threshold value when the electron blocking layer is subjected to N times of electrochemical cyclic voltammetry, wherein N is an integer greater than or equal to 30.

9. The light-emitting device according to claim 1,

the electron blocking layer has a hole mobility of greater than 10^-3cm²V^-1s^-1。

10. The light-emitting device according to claim 1,

the light emitting layer is a blue light emitting layer.

11. The light-emitting device according to claim 1,

the doping ratio of the host material to the guest material is as follows:

the concentration of the main body material is 80-99.9%;

the concentration of the guest material is 0.1-20%.

12. A light-emitting apparatus comprising the light-emitting device according to any one of claims 1 to 11.